This invention relates to a binary code encoding system for converting a sequence of binary data to a sequence of binary codes suitable for recording the original binary data on a record medium such as a magnetic tape or a magnetic disc, and a decoding system for decoding and converting the sequence of converted binary codes upon reproducing it from the record medium.
In order to increase a recording density upon recording binary data on a record medium such as a magnetic tape or a magnetic disc, there are previously proposed and practiced various encoding systems.
FIGS. 1(a)-(e) are explanatory diagrams of one example of conventional encoding systems. FIG. 1(a) shows one example of a bit pattern of an original binary data sequence wherein numerals 0 and 1 express logic "0" and "1" respectively and T.sub.o indicates a bit interval. FIGS. (b) and (d) are one example of conventional encoding systems; FIG. (b) is called an FM system and FIG. (d) is called an MFM system (a modified FM system). A conversion algorithm of the FM system is to convert bits "1" and "0" in an original binary data sequence to "11" and "10" respectively. A conversion algorithm of the MFM system is to convert bits "1" and "0" in an original binary data sequence to "01" and "X0" respectively where "X" becomes a complement logic (1.fwdarw.0 or 0.fwdarw.1) of a code bit just preceding thereto.
Furthermore a sequence of codes converted according to each of the encoding systems is such that recording currents are generated and recorded on a record medium so as to cause an inversion of magnetization with bits of "1" but not to cause an inversion of magnetization with bits of "0". FIGS. 1(c) and (e) are waveforms of the recording currents (NRZI signals) for the code sequences encoded according to the FM system of the same FIG. (b) and the MFM system of the same FIG. (d) respectively.
In the case the recording is generally effected on a record medium,
(a) if a spacing between the inversions of magnetization (a recording wavelength) is shortened, then magnetic transitions due to the leading and trailing inversions of magnetization interfere with each other so as to cause the generation of errors upon decoding a reproduced signal;
(b) even if a demodulation phase margin (Tw) (which will be described later) during the reproduction is small with respect to the spacing between the inversions of magnetization, the abovementioned errors are apt be caused; and
(c) if the spacing between the inversions of magnetization is long as compared with a period of a demodulating clock signal produced from a reproduced signal, then the demodulating clock signal can not be accurately produced from the reproduced signal and the abovementioned errors are apt to be caused;
In general encoding systems, therefore, the undermentioned variables are given as the parameters indicating the ability including the three items (a), (b) and (c) as described above. Now, assuming that in some encoding system, a sequence of m-bit binary data is converted to a sequence of n-bit binary codes (n.gtoreq.m) and, between a code bit "1" selected at will from the code sequence after the conversion and a code bit "1" next developed, there exist code bits "0" whose number has a minimum of d and a maximum of k, the following expressions (1) to (4) hold: ##EQU1## where T.sub.O is a period of the original data.
Accordingly, the foregoing description values of the expressions (1) and (4) are preferably larger (the abovementioned items (a) and (b)) and also the undermentioned ratio of the spacing between the inversions of maximum magnetization to the period of the demodulating clock signal (the expression (5)) is preferably smaller (the abovementioned item (c)). ##EQU2##
With respect to the FM system, the MFM system and the encoding system according to the present invention, the foregoing parameters are shown in the following first Table:
1ST TABLE __________________________________________________________________________ Table of Comparison of Parameters in Respective Encoding Systems Parameter Spa. btwn. Spa. btwn. Invs. of Invs. of Max. Magzn./ Max. Magzn./ Spa. Spa. btwn. Demodg. Period btwn. Invs. Mod. Invs. of Phase Demodg. of Min. System Min. Magzn. Marg. Clock Sig. Magzn. __________________________________________________________________________ FM System 0.5T.sub.0 0.5T.sub.0 4 2 MFM System T.sub.0 0.5T.sub.0 4 4 System of This Invention ##STR1## ##STR2## 9 8 __________________________________________________________________________